The major purpose of this research is to improve the usefulness of urinalysis as a measure of exposure to certain industrial poisons. Selected groups of workers with exposures to various industrial health hazards will be studied. The excretion of the toxic substance, or a suitable metabolite, will be compared with its concentration in the air, as measured wherever possible by means of personnel sampling devices. Methods of analysis which are sufficiently sensitive but reasonably simple will be developed when necessary and practicable. The influence of factors such as fluid intake, sweating and physical excretion will be studied. The results of the study will be of great importance in the development of biologic standards as a supplement to air standards, for exposures to harmful substances.